Adjusting Control Parameters for DR Election
Pre-configuration Tasks
Before configuring control parameters for DR election, complete the following tasks:
- Configure a unicast routing protocol to ensure normal unicast routing on the network.
- Enable PIM-SM.
Configuring the DR Priority
Context
The shared network segment where a multicast source or group member resides is usually connected to multiple PIM devices. PIM devices exchange Hello messages to elect a designated router (DR) on the network segment, which is the unique sender of multicast packets. The DR priorities carried in Hello messages are compared at first. The device with the highest DR priority wins (A larger value indicates a higher priority). If PIM devices have the same DR priority or at least one PIM device does not support Hello messages carrying the DR priority, the PIM device with the largest IP address wins.
The DR priority can be configured globally or on an interface. If you configure the DR priority in the global PIM view and in the interface view simultaneously, the configuration in the interface view takes effect.
Configuring the DR Switchover Delay
Context
When an interface on a shared network segment changes from a designated router (DR) to a non-DR, PIM devices on the network segment immediately delete the related multicast forwarding entries. This causes loss of multicast data in a short period. To avoid such a situation, enable DR switching delay function and set a delay time. When the DR changes, the original multicast forwarding entries are retained within the delay time.
Procedure
- Run system-view
The system view is displayed.
- Run interface interface-type interface-number
The interface view is displayed.
- Run pim timer dr-switch-delay interval
The DR switchover delay function is enabled and a delay time is configured.
By default, when the interface changes from a DR to a non-DR, the interface stops forwarding data immediately.
Verifying the Configuration of Control Parameters for DR Election
Prerequisites
After the control parameters for electing a DR are adjusted, you can check information about the PIM interface and the PIM neighbor.
Procedure
- Run the display pim [ vpn-instance vpn-instance-name | all-instance ] interface [ interface-type interface-number | up | down ] [ verbose ] command to check PIM information on an interface.
- Run the display pim [ vpn-instance vpn-instance-name | all-instance ] neighbor [ neighbor-address | interface interface-type interface-number | verbose ] * command to check information about PIM neighbors.